gdbserver: Add LoongArch/Linux support

Implement LoongArch/Linux support, including XML target description
handling based on features determined, GPR regset support, and software
breakpoint handling.

In the Linux kernel code of LoongArch, ptrace implements PTRACE_POKEUSR
and PTRACE_PEEKUSR in the arch_ptrace function, so srv_linux_usrregs is
set to yes.

With this patch on LoongArch:

  $ make check-gdb TESTS="gdb.server/server-connect.exp"
  [...]
  # of expected passes		18
  [...]

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>

gdb/NEWS

@@ -694,6 +694,8 @@ QMemTags
 
   ** GDBserver is now supported on RISC-V GNU/Linux.
 
+  ** GDBserver is now supported on LoongArch GNU/Linux.
+
   ** GDBserver no longer supports these host triplets:
 
     i[34567]86-*-lynxos*
@@ -785,6 +787,7 @@ alias [-a] [--] ALIAS = COMMAND [DEFAULT-ARGS...]
 * New targets
 
 GNU/Linux/RISC-V (gdbserver)	riscv*-*-linux*
+GNU/Linux/LoongArch (gdbserver)	loongarch*-*-linux*
 BPF				bpf-unknown-none
 Z80				z80-unknown-*
 

gdb/arch/loongarch.c

@@ -25,7 +25,13 @@
 #include "../features/loongarch/base32.c"
 #include "../features/loongarch/base64.c"
 
-static target_desc_up
+#ifndef GDBSERVER
+#define STATIC_IN_GDB static
+#else
+#define STATIC_IN_GDB
+#endif
+
+STATIC_IN_GDB target_desc_up
 loongarch_create_target_description (const struct loongarch_gdbarch_features features)
 {
   /* Now we should create a new target description.  */
@@ -51,6 +57,8 @@ loongarch_create_target_description (const struct loongarch_gdbarch_features fea
   return tdesc;
 }
 
+#ifndef GDBSERVER
+
 /* Wrapper used by std::unordered_map to generate hash for feature set.  */
 struct loongarch_gdbarch_features_hasher
 {
@@ -86,3 +94,5 @@ loongarch_lookup_target_description (const struct loongarch_gdbarch_features fea
   loongarch_tdesc_cache.emplace (features, std::move (tdesc));
   return ptr;
 }
+
+#endif /* !GDBSERVER */

gdb/arch/loongarch.h

@@ -60,6 +60,17 @@ struct loongarch_gdbarch_features
   }
 };
 
+#ifdef GDBSERVER
+
+/* Create and return a target description that is compatible with FEATURES.
+   This is only used directly from the gdbserver where the created target
+   description is modified after it is return.  */
+
+target_desc_up loongarch_create_target_description
+	(const struct loongarch_gdbarch_features features);
+
+#else
+
 /* Lookup an already existing target description matching FEATURES, or
    create a new target description if this is the first time we have seen
    FEATURES.  For the same FEATURES the same target_desc is always
@@ -70,4 +81,6 @@ struct loongarch_gdbarch_features
 const target_desc *loongarch_lookup_target_description
 	(const struct loongarch_gdbarch_features features);
 
+#endif /* GDBSERVER */
+
 #endif /* ARCH_LOONGARCH_H  */

gdbserver/Makefile.in

@@ -176,6 +176,7 @@ SFILES = \
 	$(srcdir)/linux-arc-low.cc \
 	$(srcdir)/linux-arm-low.cc \
 	$(srcdir)/linux-ia64-low.cc \
+	$(srcdir)/linux-loongarch-low.cc \
 	$(srcdir)/linux-low.cc \
 	$(srcdir)/linux-m68k-low.cc \
 	$(srcdir)/linux-mips-low.cc \
@@ -211,6 +212,7 @@ SFILES = \
 	$(srcdir)/../gdb/arch/arm.c \
 	$(srcdir)/../gdb/arch/arm-get-next-pcs.c \
 	$(srcdir)/../gdb/arch/arm-linux.c \
+	$(srcdir)/../gdb/arch/loongarch.c \
 	$(srcdir)/../gdb/arch/ppc-linux-common.c \
 	$(srcdir)/../gdb/arch/riscv.c \
 	$(srcdir)/../gdb/nat/aarch64-mte-linux-ptrace.c \

gdbserver/configure.srv

@@ -126,6 +126,12 @@ case "${gdbserver_host}" in
 			srv_tgtobj="$srv_linux_obj linux-ia64-low.o"
 			srv_linux_usrregs=yes
 			;;
+  loongarch*-*-linux*)	srv_tgtobj="arch/loongarch.o linux-loongarch-low.o"
+			srv_tgtobj="${srv_tgtobj} ${srv_linux_obj}"
+			srv_linux_regsets=yes
+			srv_linux_usrregs=yes
+			srv_linux_thread_db=yes
+			;;
   m68*-*-linux*)	if test "$gdb_cv_m68k_is_coldfire" = yes; then
                           srv_regobj=reg-cf.o
                         else

gdbserver/linux-loongarch-low.cc

@@ -0,0 +1,245 @@
+/* GNU/Linux/LoongArch specific low level interface, for the remote server
+   for GDB.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "server.h"
+#include "linux-low.h"
+#include "tdesc.h"
+#include "elf/common.h"
+#include "arch/loongarch.h"
+
+/* Linux target ops definitions for the LoongArch architecture.  */
+
+class loongarch_target : public linux_process_target
+{
+public:
+
+  const regs_info *get_regs_info () override;
+
+  int breakpoint_kind_from_pc (CORE_ADDR *pcptr) override;
+
+  const gdb_byte *sw_breakpoint_from_kind (int kind, int *size) override;
+
+protected:
+
+  void low_arch_setup () override;
+
+  bool low_cannot_fetch_register (int regno) override;
+
+  bool low_cannot_store_register (int regno) override;
+
+  bool low_fetch_register (regcache *regcache, int regno) override;
+
+  bool low_supports_breakpoints () override;
+
+  CORE_ADDR low_get_pc (regcache *regcache) override;
+
+  void low_set_pc (regcache *regcache, CORE_ADDR newpc) override;
+
+  bool low_breakpoint_at (CORE_ADDR pc) override;
+};
+
+/* The singleton target ops object.  */
+
+static loongarch_target the_loongarch_target;
+
+bool
+loongarch_target::low_cannot_fetch_register (int regno)
+{
+  gdb_assert_not_reached ("linux target op low_cannot_fetch_register "
+			  "is not implemented by the target");
+}
+
+bool
+loongarch_target::low_cannot_store_register (int regno)
+{
+  gdb_assert_not_reached ("linux target op low_cannot_store_register "
+			  "is not implemented by the target");
+}
+
+/* Implementation of linux target ops method "low_arch_setup".  */
+
+void
+loongarch_target::low_arch_setup ()
+{
+  static const char *expedite_regs[] = { "r3", "pc", NULL };
+  loongarch_gdbarch_features features;
+  target_desc_up tdesc;
+
+  features.xlen = sizeof (elf_greg_t);
+  tdesc = loongarch_create_target_description (features);
+
+  if (!tdesc->expedite_regs)
+    init_target_desc (tdesc.get (), expedite_regs);
+  current_process ()->tdesc = tdesc.release ();
+}
+
+/* Collect GPRs from REGCACHE into BUF.  */
+
+static void
+loongarch_fill_gregset (struct regcache *regcache, void *buf)
+{
+  const struct target_desc *tdesc = regcache->tdesc;
+  elf_gregset_t *regset = (elf_gregset_t *) buf;
+  int regno = find_regno (tdesc, "r0");
+  int i;
+
+  for (i = 1; i < 32; i++)
+    collect_register (regcache, regno + i, *regset + i);
+  collect_register_by_name (regcache, "pc", *regset + 32);
+  collect_register_by_name (regcache, "badv", *regset + 33);
+}
+
+/* Supply GPRs from BUF into REGCACHE.  */
+
+static void
+loongarch_store_gregset (struct regcache *regcache, const void *buf)
+{
+  const struct target_desc *tdesc = regcache->tdesc;
+  const elf_gregset_t *regset = (const elf_gregset_t *) buf;
+  int regno = find_regno (tdesc, "r0");
+  int i;
+
+  supply_register_zeroed (regcache, regno);
+  for (i = 1; i < 32; i++)
+    supply_register (regcache, regno + i, *regset + i);
+  supply_register_by_name (regcache, "pc", *regset + 32);
+  supply_register_by_name (regcache, "badv", *regset + 33);
+}
+
+/* LoongArch/Linux regsets.  */
+static struct regset_info loongarch_regsets[] = {
+  { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_PRSTATUS, sizeof (elf_gregset_t),
+    GENERAL_REGS, loongarch_fill_gregset, loongarch_store_gregset },
+  NULL_REGSET
+};
+
+/* LoongArch/Linux regset information.  */
+static struct regsets_info loongarch_regsets_info =
+  {
+    loongarch_regsets, /* regsets */
+    0, /* num_regsets */
+    NULL, /* disabled_regsets */
+  };
+
+/* Definition of linux_target_ops data member "regs_info".  */
+static struct regs_info loongarch_regs =
+  {
+    NULL, /* regset_bitmap */
+    NULL, /* usrregs */
+    &loongarch_regsets_info,
+  };
+
+/* Implementation of linux target ops method "get_regs_info".  */
+
+const regs_info *
+loongarch_target::get_regs_info ()
+{
+  return &loongarch_regs;
+}
+
+/* Implementation of linux target ops method "low_fetch_register".  */
+
+bool
+loongarch_target::low_fetch_register (regcache *regcache, int regno)
+{
+  const struct target_desc *tdesc = regcache->tdesc;
+
+  if (regno != find_regno (tdesc, "r0"))
+    return false;
+  supply_register_zeroed (regcache, regno);
+  return true;
+}
+
+bool
+loongarch_target::low_supports_breakpoints ()
+{
+  return true;
+}
+
+/* Implementation of linux target ops method "low_get_pc".  */
+
+CORE_ADDR
+loongarch_target::low_get_pc (regcache *regcache)
+{
+  if (register_size (regcache->tdesc, 0) == 8)
+    return linux_get_pc_64bit (regcache);
+  else
+    return linux_get_pc_32bit (regcache);
+}
+
+/* Implementation of linux target ops method "low_set_pc".  */
+
+void
+loongarch_target::low_set_pc (regcache *regcache, CORE_ADDR newpc)
+{
+  if (register_size (regcache->tdesc, 0) == 8)
+    linux_set_pc_64bit (regcache, newpc);
+  else
+    linux_set_pc_32bit (regcache, newpc);
+}
+
+#define loongarch_breakpoint_len 4
+
+/* LoongArch BRK software debug mode instruction.
+   This instruction needs to match gdb/loongarch-tdep.c
+   (loongarch_default_breakpoint).  */
+static const gdb_byte loongarch_breakpoint[] = {0x05, 0x00, 0x2a, 0x00};
+
+/* Implementation of target ops method "breakpoint_kind_from_pc".  */
+
+int
+loongarch_target::breakpoint_kind_from_pc (CORE_ADDR *pcptr)
+{
+  return loongarch_breakpoint_len;
+}
+
+/* Implementation of target ops method "sw_breakpoint_from_kind".  */
+
+const gdb_byte *
+loongarch_target::sw_breakpoint_from_kind (int kind, int *size)
+{
+  *size = loongarch_breakpoint_len;
+  return (const gdb_byte *) &loongarch_breakpoint;
+}
+
+/* Implementation of linux target ops method "low_breakpoint_at".  */
+
+bool
+loongarch_target::low_breakpoint_at (CORE_ADDR pc)
+{
+  gdb_byte insn[loongarch_breakpoint_len];
+
+  read_memory (pc, (unsigned char *) &insn, loongarch_breakpoint_len);
+  if (memcmp (insn, loongarch_breakpoint, loongarch_breakpoint_len) == 0)
+    return true;
+
+  return false;
+}
+
+/* The linux target ops object.  */
+
+linux_process_target *the_linux_target = &the_loongarch_target;
+
+/* Initialize the LoongArch/Linux target.  */
+
+void
+initialize_low_arch ()
+{
+  initialize_regsets_info (&loongarch_regsets_info);
+}